1. Field of the Invention
The present invention relates to an instrument for measuring information on an inner living body with light.
2. Description of the Related Art
The development of a technique capable of measuring information about an inner living body with ease and without noninvasion on the living body has been long expected in the fields of clinical medicine and brain science or the like. Described specifically, as exemplary measurements for the brain, may be mentioned, measurements on brain diseases such as cerebral infarction, cerebral hemorrhage, and measurements on high-order brain functions such as thought, language, motor, etc. The object to be measured is not necessarily limited to the brain. Measurements for the chest may include heart diseases such as myocardial infarction, etc. and measurements for the abdomen may include prevention and diagnosis against internal diseases such as kidney, liver disorder, etc.
When the intracerebral diseases or high-order brain functions are measured with the brain as the object to be measured, it is necessary to definitely measure a disease part or a functional region. Therefore, it is of very importance that a wide region in the brain is measured as image information. As an example indicative of this importance, may be mentioned a positron emission tomography (PET) system used as an intracerebral imaging measurement system, and a functional magnetic resonance imaging (fMRI) system, which are now widely used. These systems have drawbacks in that although they have an advantage that the wide region in the living body can be measured as the image information, they are large in size and their handling is cumbersome. For example, a dedicated room is required to install these systems and the systems are not easy to move as a matter of course. Thus, restraint on a subject is enhanced. Further, since persons dedicated to maintenance are required, considerable costs are required for practical use of these systems.
The optical measurement technique holds great promise from the above point of view. A first reason of its promise is that the normality and abnormality of organs and the brain activity about the high-order brain function are closely related to oxygen metabolism and blood circulation inside the living body. The oxygen metabolism and blood circulation correspond to the concentration of specific chromophones (such as hemoglobin, cytochrome aa.sub.3, myoglobin) in the living body. The concentration of chromophones can be determined from the absorbance of visible-infrared region light. Further, second and third reasons why the optical measurement technique is effective, are that the light can be easily handled owing to optical fibers and does no harm to the living body due to the use of the light within a safety standard range. Thus, the optical measurement technique has advantages of real time measurements and quantification of the concentration of the chromophones in the living body, and the like that the PET and fMRI lack. Further, the optical measurement technique is suitable for size reductions in the systems and simplicity of their handling.
An instrument capable of irradiating a living body with visible-infrared region light and detecting light (reflected light) subject to absorption and scattering inside the living body and discharged to the outside of the living body to thereby measure information on the inner living body, using the advantages of the optical measurement technique, has been described in, for example, Japanese Patent Application Laid-Open Nos. 57-115232, 63-260532, 63-275323 and 5-317295.
However, in the aforementioned conventional living body measurement technique using the light, the information can be measured only at a specific position in the living body or within a restricted narrow region. Therefore, imaging about a wide spatial region inside the living body has not been taken into consideration.
Specific problems about an optical measurement method and a layout configuration of light incident positions and light detection positions, which are employed in the prior art, will now be described.
The optical measurement method will first be described. It is necessary to irradiate many positions with light and detect it at many points upon imaging in the wide spatial region. One example of this type of multiposition measurement will be explained in brief with reference to FIG. 2. The present example shows the case in which lights are applied or irradiated from three points (incident positions IP1, IP2 and IP3) on the surface of a subject and the lights reflected therefrom are detected at three points (detection positions DP1, DP2 and DP3) on the surface of the subject. Measurement positions must be specified upon imaging. Light propagation in scattering media (e.g., living body) has been reported by, for example, [N. C. Bruce; "Experimental study of the effect of absorbing and transmitting inclusions in highly scattering media", Applied Optics, vol. 33, no. 28, pp. 6692-6698, (October 1994)]. Its experimental results are shown in FIG. 3. It is known from FIG. 3 that the neighborhood of a middle point between a light incident position and a light detection position includes information about a position deep from the surface of the living body. Thus, when the deep position in the living body, e.g., a deeper position of skin or skull, for example, is measured from above the skin, the middle position between the incident position and the detection position results in a measurement position. Such measurement needs to provide the incident positions and the detection positions one by one in pairs and obtain information at measurement positions (measurement positions MP1, MP2 and MP3) specified every individual pairs.
Now consider, for example, a case in which in the layout configuration shown in FIG. 2, the lights are simultaneously applied from the three incident points (incident positions IP1, IP2 and IP3) and the lights reflected therefrom are simultaneously detected at the three light detection points (detection positions DP1, DP2 and DP3). In this case, it is necessary to accurately measure only the reflected light of the light applied from the incident position IP2 at the detection position DP2 upon measurement at the measurement position DP2 corresponding to the middle point between the incident position IP2 and the detection position DP2. However, the light detected at the detection position 2 actually includes the reflected lights of the lights incident from the incident positions IP1 and IP3 as well as the reflected light of the light incident from the incident position IP2. As a result, so-called crosstalk is produced. Accordingly, only the reflected light of the light incident from the incident position IP2 cannot be separated and detected at the detection position DP2, so that the accurate measurement on the measurement position MP2 cannot be carried out.
Thus, if a switch or the like is used so as to successively switch between the incident positions every measurement positions on a time-sequence basis, such crosstalk is prevented from occurring. However, in order to successively switch between many incident positions, much time is required correspondingly upon their switching. Therefore, a long time is required for measurement, so that the measurement is rendered inefficient.
Thus, there has been a strong demand for the development of a simultaneous multichannel measurement technique capable of performing measurements on a large number of measurement positions in a subject simultaneously and without crosstalk in order to make imaging about a wide spatial region in the subject.
It is also necessary to measure information about an inner brain covered with a head scarf skin and a skull fracture with high sensitivity and satisfactory efficiency upon intra-living body measurement, particularly brain functional measurement. In the optical measurement method, the information on the deep position in the living body is detected at the middle position between the light incident position and the light detection position. If a plurality of pairs of light incident positions and light detection positions are disposed on the circumference surrounding measured portions and middle-point positions between the respective pairs are placed in common use, as a method of measuring the deep position information with high sensitivity, i.e., measuring the deep position information so that the deep position information is contained in more plenty, information on the deep position in the living body, which corresponds to each common middle-point position, can be measured with high sensitivity. Even in this case, however, the simultaneous measurement, i.e., the simultaneous multichannel measurement on the aforementioned plurality of pairs of light incident positions and light detection positions must be executed to perform the measurement in a short time and with satisfactory accuracy.
Moreover, the operations of various apparatuses typified by a computer and the input of information are now performed via a keyboard or a switch and the like. However, there may be cases in which a physically handicapped person encounters difficulties in performing such operations and information input work. There may also be cases where even a normal person cannot always take quick and appropriate measures in case of emergency of the driving of a vehicle and the operation of a large-scale plant, for example. If, in such a case, the operator can take quicker and more appropriate measures before the limbs of the operator show reactions, it is then possible to beforehand prevent serious accidents from occurring. Therefore, a method of measuring the state of activity of a function of perception and cognition in the operator's brain in real time and directly inputting a signal about a change of brain activity referred to above to the above-described various apparatuses is considered. However, the measurement of the brain activity with high sensitivity and high accuracy is indispensable to the reliable execution of the operation by such a method. Therefore, a technique for performing the aforementioned multichannel simultaneous measurement without the crosstalk is also required.